Lead titanate pyroelectric infra-red intensity detector

ABSTRACT

An infra-red intensity detector which comprises a polarized ceramic substrate composed of PbTiO3, MnO2 of from 0.8 to 1.2 mol percent of PbTiO3, and La2O3 of from 1.0 to 2.0 mol percent of Pb TiO3, and at least one couple of electrodes connected to the ceramic substrate and disposed in the direction of polarization of the substrate.

ted States Patent 11 1 Yamaka et a]. Nov. 20, 1973 LEAD TITANATE PYROELECTRIC [56] References Cited INFRA-RED INTENSITY DETECTOR UNITED STATES PATENTS [75] Inventors: Eiso Yamaka; Ichiro Ueda, both of 2,985,700 5/1961 Johnston 136/239 Kadoma City, J an 3,673,119 6/1972 Ueoka et a1. 252 520 3,511,991 5/1970 Beerman 250/833 H [73] Ass1gnee: Matsushita Electric lndusrial 3,453 432 7 1969 McHenry 136/213 UX Company, Limited, Kadoma City, 3,458,363 7/1969 Precht 136/238 Osaka, Japan Primary ExaminerCarl D. Quarforth [22] Filed Man 1972 Assistant ExaminerE. A. Miller [21] Appl. No.: 235,649 Att0rneyJ0hn Lezdey et a].

[30] Foreign Application Priority Data [57] f ABSTRACTh h An in ra-red intensity detector w ic comprises a po M l ar 971 Japan 46/15901 lanzed ceramic substrate composed of PbT1O MnO 52 US. (:1 136 213 136 236 136 23s fmm Percent T and 1 136/239 250/8; 3 d of from 1.0 to 2.0 mol percent of Pb T10 and at least [51] Int CL nolv 3/00 one couple of electrodes connected to the ceramic [58] Fie'ld 239 236 substrate and disposed in the direction of polarization of the Substrate.

1 Claim, 2 Drawing Figures LEAD TITANATE PYROELECTRIC INFRA-RED INTENSITY DETECTOR This invention relates to infra-red intensity detectors and, more particularly, to an infra-red intensity detector utilizing pyroelectricity.

An infra-red intensity detector sensitive to infra-red rays is useful for detecting relatively low temperature or temperature distribution of a surface of a material from a position remote from the surface of the material since the surface of the material of relatively low temperature radiates infra-red rays residing in a spectrum where a peak value locates at a wavelength of about l microns.

Various infra-red detectors sensitive to infra-red rays have been developed, one of which is of photoconductive type such as a germanium infra-red detector. This type detector has an excellent sensitivity and a high responsiveness, although this type detector is disadvantageous in that the detector is workable merely in a limited wavelength range and operative only at a low ambient temperature. Another infra-red detector is a thermistor bolometer. Although thermistor bolometer is workable in wide wavelength range and operative at a high ambient temperature, the thermistor bolometer should be, in operation, impressed by a bias voltage :t 100 to 300 V. Still another infra-red detector is of pyroelectric type utilizing pyroelectric crystal which are spontaneously polarized in dependence on temperature variation of the crystal caused by infra-red rays irradiated thereto. The pyroelectric infra-red intensity detector is workable in a wide wavelength range and is operative at an either low or high temperature without any bias voltage. It is known in the art that the pyroelectric effect takes place in the following crystals: barium titanate, lithium sulfate. Rochelle salt (KNaC H O lead titanate zirconnate, tri-glycine sulfate (TGS), lithium niobate (LiN- bO SKL (Sr,KLiNb O and SBN (Sr,Ba, Nb O Heretofore, the TGS, LiNbO and SBN have often been used for the infra-red detectors.

In this instance, it is to be noted that a pyroelectric crystal to be used for an infra-red intensity detector should be discussed from the following view points:

i. Detectivity (D*) Detectivity D* ofa pyroelectric crystal is represented by a reciprocal of such an intensity of infra-red rays incident upon the crystal as to cause a pyroelectric signal having an intensity equal to that of noise produced in the crystal to appear in the crystal. The demension of the Detectivity is expressed by cm. VHz/W.

2. Formability Formability of a pyroelectric crystal generally governs mass-productivity and prodution cost thereof. It is desired that the crystal to be used for the infra-red detector is readily formed into a small wafer of about 1 x l X 0.02 mm in volume through cutting or polishing treatment. It is further desired that electrodes for picking-up pyroelectric effect is readily adhered onto the surface of the crystal.

3. Curie temperature (Tc) Since the spontaneous polarization in the pyroelectric crystal might be possible only below the Curie temperature, the pyroelectric detector should be used below the Curie temperature. Therefore, it is desirable that a pyroelectric crystal to be used for an infra-red intensity detector has a high Curie temperature.

4. Temperature coefficient of the spontaneous polarization (dPs/dT) Temperature coefficient of spontaneous polarization of a pyroelectric crystal governs sensitivity of the device including the crystal.

TGS, LiNbO and SBN crystals will be discussed from the above-mentioned view points in the following description.

1. tri-glycine sulfate (TGS) Since tri-glycine sulfate crystal is so brittle that it may be difficult to form the crystal into a desired shape. Furthermore, since tri-glycine sulfate crystal is soluble in water, the crystal is susceptible to moisture in the atmosphere. Therefore, the crystals should be in fabrication protected from influence of the moisture in the ambient air and the device should be provided with a shield case for containing the crystal therein.

Furthermore, since the glicinium sulfate crystal has such a low Curie temperature as 50C, the detector using the crystal is operative merely at from 30 to 40C.

2. lithium niobate (LiNbO Although lithium niobate crystal has a preferred formability and high Curie temperature, the crystal has poor detectivity D* even if the crystal is a single crystalline.

It is difficult to obtain a high quality single crystalline of SBN. Although the SBN crystal has a preferred detectivity D*, the crystal has a low Curie temperature. It is further difficult to polarize the SBN crystal in one direction.

Being apparent from the above-description, the conventional pyroelectric infra-red detectors using abovementioned crystals are not fully acceptable.

It is therefore an object of the present invention to provide an improved pyroelectric infra-red intensity detector.

It is another object to provide an infra-red intensity detector having a sufficiently large detectivity D*.

It is still another object to provide an infra-red intensity detector having a preferred formability.

It is a further object to provide an infra-red intensity detector having a high Curie temperature.

It is a still further object to provide an infra-red intensity detector which is readily fablicated through a massproductive process.

Further and another objects of the invention will be more clearly apparent by reference to the following description, taken in conjunction" with the accompanying drawing in which:

FIGS. 1 and 2 are sectional views of preferred embodiments of the present invention.

Corresponding numerals of reference designate like elements in the views.

An infra-red intensity detector according to the present invention utilizes a polarized ceramic substrate composed of PbTiO MnO, of 0.2 mol percent of the PbTiO and La O of 1.0 to 2.0 mol percent of the PbTiO it is apparent from the following Table that the pyroelectric material according to the invention has a characteristic superior to those of the conventional pyroelectric material.

TABLE Curie telngii D dPs Coul. cm. Material C C.) cm. UAW) dT Cal Forllldblljl} TGS. r 5. 6X19 3.5)( Poor, soluble in water. LiNbu; 2 i0= 043x10 SBN i r 22.5)(10 6X10 PbTiOg plus Milt); and L320; ceram 9. 5X10 6X10 Excellent.

Referring now to FIG. 1, there is illustrated an embodiment of an infra-red intensity detector according to the invention, which comprises a infra-red sensitive element 10 including a pyroelectric polarized ceramic substrate 12 composed of PbTiO MnO of 0.8 to 1.2 mol percent of PbTiO and La O of 1.0 to 2.0 mol percent of PbTiO The substrate 12 is polarized in a direction indicated by arrows A. A pair of electrodes 14 and 14' made of, for example, gold nichrome or aluminium are formed on both the major surface of the substrate 12 through a suitable process such as vacuum evaporation. in this instance, it is necessary to align the electrodes 14 and 14' in the direction of polarization of the substrate 12. A pair of lead wires 16 and 16' are connected to the electrodes 14 and 14, respectively, for the sake of picking-up of variation of the polarization as an electric signal. The infra-red sensitive element [0 is mounted through, for example, the electrode 14' on a support member 18 which is in turn secured to an inner wall of a housing (not shown) of the detector so as to block heat transfer from the infra-red sensitive element 10 to the housing.

When, in operation, infra-red rays are irradiated onto the surface of the substrate 12 as shown by an arrow B, the polarization of the substrate 12 is varied in dependence on the intensity of the irradiated infra-red rays. The variation of the polarization is picked-up through the electrodes 14 and 14 and lead wires 16 and 16' as an electric signal which is sensed by, for example, a voltage meter. When the electrode 14 is made so thin as to permit infra-red rays to permeate therethrough, the infra-red sensitive element 10 can detect infra-red rays incident on the electrode 14 as shown by an arrow C.

In FIG. 2, another embodiment of the infra-red intensity detector of the invention is illustrated. which is constructed identically to that of FIG. 1, except that the substrate 12 is mounted on the support member 18. This detector is sensitive to infra-red rays incident to the substrate as shown by an arrow D.

A preferred method of making the substrate 12 will explained hereinafter.

A mixture of PhD and TiO equimolecular to PbO is first prepared. The mixture is then mixed through a wet mixing process with MnO of 0.8 to 1.2 mol percent of pbTiO and La O of 1.0 to 2.0 mol percent of PbTiO Thereafter, the resultant mixture is calcined at about 850C. The thus calcined mixture is then pulverized into a fine powder. The fine powder is formed into pellet or disk shape and sintered at a temperature from 1240" to 1280C in the air during about 1 hour. The resultant ceramics are dipped in a silicon oil bath of 200C where an electric fieldfof about KV/cm is established, so that, the ceramics are polarized. The polarized ceramics are formed into a desired shape.

It is apparent from the foregoing description that the infra-red detector according to this invention is advantageous in its high detectivity D* and Curie temperature. Furthermore, the infra-red detector has excellent formability.

It will be understood that the invention is not to be limited to the exact construction shown and described and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

1. An infra-red intensity detector comprising a polarized ceramic substrate consisting of a mixture of PbTiO MnO in an amount from 0.8 to 1.2 mol percent of said PbTiO and La O in an amount from 1.0 to 2.0 mol percent of said PbTiO and a pair of electrodes connected to opposite sides of said ceramic substrate, said electrodes being provided in the direction of polarization of said substrate. 

